Certain chiral 3,4-disubstituted piperidines are pharmaceutically-active. The desired activity normally resides in only one of the single isomeric forms. In particular, the trans-(3S,4R)-isomer of such a compound, where the 3-substituent is 4-fluorophenyl and the 4-substituent is 3,4-methylenedioxyphenoxymethyl, i.e. paroxetine, is a potent anti-depressant drug that is widely prescribed for the treatment of depression.
Existing methods for the synthesis of single isomer paroxetine involve a resolution step. This means that the unwanted enantiomer, following resolution, is either wasted or must be converted to the desired enantiomer by an inversion process.
Willcocks et al, Journal of Labelled Compounds and Radiopharmaceuticals (1993) XXXIII(8):784-94, disclose the synthesis of .sup.14 C-labelled paroxetine. A key intermediate in this synthesis is 4-(4-fluorophenyl)-3-hydroxymethyl-1-methylpiperidine, obtained by reduction of the tetrahydropyridine. This key intermediate is converted to paroxetine by reaction with benzenesulphonyl chloride, then sesamol (with inversion), and removal of the N-methyl group. The starting material for the synthesis is a neurotoxin.
Mangeney et al, J. Org. Chem. (1994) 59:1877-85, disclose an asymmetric synthesis of 3-formyl-1,4-dihydropyridines, comprising the addition of organocopper reagents to activated 3-imidazolidinylpyridine, prepared using chiral diamines. This methodology was used for the asymmetric synthesis of indoloquinolizine and benzoquinolizine alkaloid frameworks.